WASHINGTON — President Trump rejected, for now at least, a fresh round of sanctions set to be imposed against Russia on Monday, a course change that underscored the schism between the president and his national security team.

The president’s ambassador to the United Nations, Nikki R. Haley, had announced on Sunday that the administration would place sanctions on Russian companies found to be assisting Syria’s chemical weapons program. The sanctions were listed on a menu of further government options after an American-led airstrike on Syria, retaliating against a suspected gas attack that killed dozens a week earlier.

But the White House contradicted her on Monday, saying that Mr. Trump had not approved additional measures.

“We are considering additional sanctions on Russia and a decision will be made in the near future,” Sarah Huckabee Sanders, the White House press secretary, said in a statement.

Speaking later with reporters aboard Air Force One as Mr. Trump headed to Florida, Ms. Sanders added that “the president has been clear that he’s going to be tough on Russia, but at the same time he’d still like to have a good relationship with them.”

Another White House official, who spoke on condition of anonymity to describe internal deliberations, said Mr. Trump had decided not to go forward with the sanctions. Mr. Trump concluded that they were unnecessary because Moscow’s response to the airstrike was mainly bluster, the official said.

Russia analysts said the whipsaw policy shift once again highlighted an administration struggling to find a coherent and consistent voice in dealing with Russia, which in the past four years has annexed Crimea, intervened in eastern Ukraine, sought to influence the American election in 2016, allegedly poisoned a former Russian spy living in Britain and propped up the murderous government of President Bashar al-Assad in Syria.

Mr. Trump has mostly spoken hopefully of his efforts to forge a friendship with President Vladimir V. Putin of Russia, including congratulating him on a re-election widely denounced as a sham and even suggesting a White House meeting. At the same time, the Trump administration has imposed two rounds of sanctions against Russia in the last month, expelled 60 of Moscow’s diplomats and closed a consulate in retaliation for the poisoning attack in Britain.

“Trump seems to think that if he accepts what his advisers recommend on even days of the month and rejects their recommendations on odd days, the result will be a strategy,” said Stephen Sestanovich, a scholar at the Council on Foreign Relations and Columbia University who served as ambassador to former Soviet states in the 1990s.

“By and large, other governments don’t know whether to laugh or cry at all this,” Mr. Sestanovich said. “But in Russia, laughter is getting the upper hand.”

Mr. Trump was annoyed with Ms. Haley for getting out in front of the policy, the administration official said, and the president’s decision to reject sanctions left her hanging in public with her credibility on the line.

Ms. Haley has been one of the strongest critics in the administration of Russia’s behavior around the world, often speaking far more harshly than Mr. Trump would, but she has rarely been reined in publicly this way. She made no comment on Monday.

Administration officials said new sanctions could still be imposed at some point if Russia takes further action justifying them.

But absent such a scenario, the officials could not explain how Mr. Trump would make Russia pay a “big price” for enabling Syria’s use of chemical weapons, as he promised to do last week after a suspected gas attack killed more than 40 people and sickened scores more outside Damascus on April 7.

The strike against Syria that Mr. Trump announced late Friday in Washington was limited to a single night and to three targets linked to chemical weapons facilities. It sought to punish President Bashar al-Assad of Syria for the suspected gas attack but avoid provoking Russia into a response.

Russia responded harshly to the news of sanctions before learning that Mr. Trump had canceled them. “The sanctions drive against Russia is becoming an obsession,” Dmitri S. Peskov, the Kremlin spokesman, told reporters at his daily briefing in Moscow. “We’re convinced that any economist can see open attempts to squeeze Russian companies out of global markets.”

Critics said the president’s decision not to follow through on Ms. Haley’s announcement would sap American authority around the world.

“I am outraged that President Trump pulled back sanctions on Russia for its support of the Assad regime,” said Representative Eliot L. Engel of New York, the senior Democrat on the House Foreign Affairs Committee. “This sends a message to governments around the world that they can support brutal, criminal behavior without serious consequences.

“President Trump is out of step with the American people, American values — and as this situation has made clear, his own administration,” Mr. Engel said.

The about-face on sanctions came a day after ABC News broadcast an interview with James B. Comey, the former F.B.I. director fired by Mr. Trump last year, in which he said he thought “it’s possible” that the president had been compromised by Russia. A protester waiting for Mr. Trump in Florida on Monday held a large banner that read, “Russian stooge.”

Mr. Trump has heatedly and repeatedly denied any collusion with Russia during his 2016 campaign, calling such suggestions a “hoax” perpetrated by Democratic sore losers desperate to explain an election defeat.

Russia did not respond militarily to the Friday strike, but American officials noted a sharp spike in Russian online activity around the time it was launched.

A snapshot on Friday night recorded a 2,000 percent increase in citing the hashtag #isupportsyria on Russian troll networks, according to a senior official at the Department of Homeland Security who was not authorized to discuss the issue by name and spoke on condition of anonymity. Additionally, the official said, the known Russian hashtag #SyriaStrikes had a 4,443 percent increase in activity while another, #Damsucs, saw a 2,800 percent jump.

In hitting the Barzah Research and Development Center, a chemical weapons research lab in greater Damascus, and two storage facilities and bunkers near Homs, Pentagon officials insisted that they dealt a critical blow to Mr. Assad’s weapons program. But Friday night’s strike, delivered via 105 missiles, was not quite double the 59 missiles used last year when Mr. Trump ordered the military to strike a Syrian airfield from which planes engaged in another chemical weapons attack took off.

Defense Secretary Jim Mattis pushed hard to limit the strikes to proven weapons facilities in the hopes that a more limited strike would not prompt retaliation from Russia.

The lab at Barzah, in Damascus, was on the receiving end of the biggest barrage — some 76 missiles, a combination of Tomahawk cruise missiles and Joint air-to-surface missiles. The rest of the bombs — 29, fired by American, French and British warplanes — struck and destroyed the Him Shinshar chemical weapons storage facility near Homs, and the Him Shinshar chemical weapons bunker facility around five miles away.

Syria tried to hit back, but by the time its air defense system was deployed, the American warplanes were on their way home and the war ships had completed their mission, military officials said. They disputed Syrian claims to have shot down dozens of American missiles.

“We assess that over 40 surface-to-air missiles were employed by the Syrian regime,” Lt. Gen. Kenneth F. McKenzie, director of the Joint Staff at the Pentagon, told reporters on Saturday. “Most of these launches occurred after the last impact of our strike was over.”

He called the Syrian retaliatory missiles “largely ineffective” and said they “clearly increased risk to their own people based on their indiscriminate response — when you shoot iron into the sky without guidance, it will inevitably fall to earth.”

Correction:

An earlier version of this article, relying on information provided by a senior official at the Department of Homeland Security, referred incorrectly to an increase of Russian online trolling activity that occurred on the same day as airstrikes against Syria. The increase was noted among Russian hashtags, not bots. Additionally, the information should not have been attributed to the department’s spokesman, Tyler Q. Houlton.

Reporting was contributed by Neil MacFarquhar and Ivan Nechepurenko from Moscow and Helene Cooper and Ron Nixon from Washington.

Follow Peter Baker on Twitter: @peterbakernyt

A version of this article appears in print on , on Page A1 of the New York edition with the headline: Trump Declines To Add Sanctions Against Russians. Order Reprints | Today’s Paper | Subscribe